The United States is evolving into a Big Brother society as technology advances and post-Sept 11 surveillance increases, the American Civil Liberties Union said in a new report.

"The reasonable expectation of privacy has been dramatically diminished," Barry Steinhardt, an ACLU director, said in an interview following Wednesday's release of the report "Bigger Monster, Weaker Chains: The Growth of an American Surveillance Society."

"A combination of lightning-fast technological innovations and the erosion of privacy protections threatens to transform Big Brother from an oft-cited but remote threat into a very real part of American life," the report said.

A growing "surveillance monster" is emerging, it argues, in which the private and the public sector are monitoring Americans with video cameras to the extent that it is becoming almost impossible to walk the streets of major cities without being filmed. Yet there are virtually no rules governing what can be done with those tapes.

Computer chip technology currently in use to speed motorists through tollbooths might one day be used on identification cards to allow police officers to "scan your identification when they pass you on the street," the report said.

The study points to the Total Information Awareness pilot project, in which the Pentagon is exploring amassing a database of Americans' medical, health, financial, tax and other records. There are few privacy laws to prevent businesses from selling the government such information, Steinhardt said.

"If we do not act to reverse the current trend, data surveillance — like video surveillance — will allow corporations or the government to constantly monitor what individual Americans do every day," the report said.

Moreover, under the Patriot Act — the anti-terrorist legislation passed by Congress immediately after the Sept. 11 attacks — the government can demand that libraries turn over reading habits of patrons. Authorities can more easily attain telephone and computer wiretaps, and conduct searches in secret without immediately notifying the target.

Viet Dinh, an assistant U.S. attorney general and one of the government's spokesmen on security topics, said in a recent interview that the Bush administration would not abuse these far-reaching powers.

"I think security exists for liberty to flourish and liberty cannot exist without order and security," Dinh said.

New rules, the report notes, reinstate the FBI's ability to spy on Americans even when no crime is suspected and allows authorities to share with prosecutors information obtained via search warrants granted by the Foreign Intelligence Surveillance Act court. Under FISA court rules, Americans are not protected by the bread-and-butter legal standard of probable cause — prosecutors need only say the search will assist a terror probe.

"It is not just the reality of government surveillance that chills free expression and the freedom that Americans enjoy," the report said. "The same negative effects come when we are constantly forced to wonder whether we might be under observation."